1. Field of the invention:
This invention relates to an electronic musical instrument and more particularly to expression control means in an electronic musical instrument.
2. Description of the prior art:
Conventionally, expression control means have been used for controlling the tone volume in electronic musical instruments. The expression control means is connected between the output of the tone coloring circuit and the input of the amplifier and comprises a photoconductive element (variable resistance element) such as CdS element and a light source such as a lamp or a light emitting diode disposed opposite to each other with a shutter plate disposed therebetween. The shutter plate has a through hole of a predetermined shape and is interlocked with a foot plate for the expression control so that the amount of light impinging on the photoconductive element continuously varies according to the depth of the foot plate depression. Thus, the resistance of the photoconductive element is varied according to the depth of the foot plate depression. Hence, the signal level derived from the tone coloring circuit is controlled by the foot plate depression to effect the expression control. The tone volume increases as the expression foot plate is depressed.
According to the conventional expression control means, however, the depression angle of the expression foot plate and the tone signal level are related in one-to-one correspondence and the variation characteristic is constantly represented by a single curve and the values of the dynamic range and the minimum (or maximum) level are fixed and little, if at all varied.
Therefore, in an ensemble play, etc., it is very difficult to carry out the optimum tone volume control. Namely, when one wishes to play the instrument in a narrow tone volume range he should produce expression by minute variations of the foot plate depression, whereas to play the instrument in a wide tone volume range he should manipulate the foot plate almost from the minimum position to the maximum position. Hence, well-trained skill is required for the manipulation of the foot plate.
Further, in such an electronic musical instrument having a plurality of tone generating systems, e.g. one for strings, one for flute, etc., when the plurality of tone generating systems is operated simultaneously to provide musical sounds of a plurality of instruments, the tone volume control by the manipulation of an expression foot plate becomes common for the respective tone generating systems. Hence, musical play rich in musicality cannot be achieved.
In other words, although an electronic musical instrument has an advantage that one can perform a musical play resembling an ensemble play by a plurality of players, it cannot give variations of musical tones nor accents due to the differences in the dynamic ranges of the tone volumes of the respective musical instruments. Usually, the dynamic range of the tone volume is largest for the melody instrument. In conventional electronic musical instrument, however, performance effect due to the variations in the dynamic range has not been provided.
Further, it has been also proposed to dispose a plurality of photoconducting elements against a light source with shutter plates of predetermined shape intervening therebetween. However, the number of shutter plates interlocked with an expression foot plate is at most two. Thus, to afford expression control for more than two tone generating systems is practically impossible according to this method. It can be thought of to provide an expression foot plate for each tone generating system. This leads to very complicated manipulation and musical performance rich in variety cannot be easily achieved.
To solve the above problem, it has been recently proposed to dispose the ends of a plurality of optical fibers against a light source through a shutter plate and a plurality of photoconducting elements at the other ends of the optical fibers. These photoconducting elements are connected in the circuits for controlling the signal levels in the respective tone signal generating systems. Thus, the tone volume control for a plurality of tone signal generating systems can be achieved by the manipulation of a single expression foot plate. Such a system can achieve the tone volume control of a plurality of tone signal generating systems by a single expression foot plate, but because of the use of optical fibers it is accompanied by the practical inconveniences, such as troublesome manufacture, larger size or higher cost.